Golden Gate does not complete installation process. Asks to log into iCloud on restart and turn of File Vault, every time.

The behaviour described is unusual after a macOS installation. Seeing the “Welcome to macOS”/Setup Assistant screens after every restart, being repeatedly asked to sign in to iCloud, and being asked to enable FileVault when it is already enabled warrants further troubleshooting.

First, go to System Settings >> General >> Software Update and install any available macOS 27 update if available.

Then verify FileVault in System Settings >>Privacy & Security >> FileVault. 

You can also open Terminal and run: sudo fdesetup status

“FileVault is On” means FileVault encryption is enabled and active on the boot volume; 

“FileVault is Off” means it is not currently enabled. 

If encryption or decryption is in progress, the command may also report its progress. 

If it reports “FileVault is On,” there is generally no reason to turn FileVault off and back on simply because Setup Assistant asks you to enable it.

If this Mac is managed by a company or school, check System Settings >> General >> Device Management for a management profile. 

Device management can configure Setup Assistant and FileVault. If this is a personal, unmanaged Mac, this check can be skipped.

Next, start the Mac in Safe Mode, log in, and restart normally. 

Check whether Setup Assistant appears again.

If the problem continues, create a temporary administrator account and repeat the restart test from that account. 

If Setup Assistant also appears there, the behaviour is not limited to the original user account. 

If it does not, that difference provides useful diagnostic information.

Because this is an Apple-silicon Mac, you can also run Apple Diagnostics. 

Shut down the Mac, press and hold the power button until the startup options appear, then press Command-D. 

Follow any instructions shown and note any reference codes. Apple describes this procedure here: How to use Apple Diagnostics to test your Mac

If the problem persists, start macOS Recovery.

In Recovery, open Disk Utility, choose View >> Show All Devices, and run First Aid on each volume, then each container, and finally the physical storage device. 

Apple provides the complete procedure here: Repair a storage device in Disk Utility on Mac

If the problem remains after these checks, the next step before erasing the Mac would be to reinstall macOS from Recovery without erasing the existing installation. 

Apple states that reinstalling macOS this way does not remove apps or personal data, although making a backup beforehand is recommended: How to reinstall macOS

If macOS installation continues to fail after these steps, 

Apple also documents additional recovery options for persistent installation problems, including a firmware revive or restore for certain Apple-silicon Macs. That would be a later step rather than something to attempt initially. (Apple Support)

The above procedure will require another compatible computer

I would avoid manually deleting .AppleSetupDone or modifying files in /var/db at this stage. Those changes affect macOS setup state and are not necessary for the initial troubleshooting.